In recent engine designing, a downsizing concept shifted from a conventional concept with a high regard to top performance is becoming mainstream. In progress is changeover to supercharged engines in which engine displacement and a number of cylinders are reduced by supercharging with a turbocharger to obtain an output and a torque equivalent to those of natural intake engines with a size larger than the supercharged ones.
For example, in diesel engines, V-twelve and -eight engines used to be prevailing in particular with respect to commercial vehicles (trucks). Now, supercharged straight-six and -four engines are becoming mainstream owing to the downsizing concept.
In association with such downsizing concept being becoming main stream, further compactification in size of turbochargers has been demanded, which makes it difficult to arrange a rotation sensor at a bearing portion between a turbine and a compressor of a turbocharger as ever.
Specifically, in the conventional rotation sensor, a disc with a circumferential notch is integrally fitted over a rotary shaft interconnecting the turbine and the compressor of the turbocharger. Arranged adjacent to the disc is a non-contact sensor which grasps passing of the notch of the disc as, for example, change in a magnetic field so that the passing of the notch of the disc is detected and counted by the sensor, whereby a rotational frequency of the turbocharger can be monitored. However, cases increase where no spatial room is left between the turbine and the compressor due to pipings of, for example, cooling water and lubrication oil so that the disc and the non-contact sensor cannot be physically arranged.
There exists, for example, the following Patent Literature 1 as conventional art document pertinent to the invention.